The Great Britain patent 1136214 disclosed compounds represented by the following formula:
wherein R1 is hydrogen or methyl, R2 is cyclopropyl methyl or allyl, R3 is alkyl, phenyl or phenyl alkyl. These compounds have potent central analgesic activity and opiate antagonist activity.
Among them, buprenorphine (where R1 is hydrogen, R2 is cyclopropyl methyl, R3 is tert-butyl) has good analgesic activity and little dependence with potency 25–30 times as that of morphine and less dependence. It has now been widely used as analgesics and anti-addiction. But buprenorphine only have moderate efficacy (40% that of morphine) and low bioavailability. So it could not be administered orally.
